The present disclosure relates to a medical imaging device, a medical image acquisition system, and an endoscope apparatus.
In recent years, observation methods for performing special light observation with special light have been devised separately from normal observation with white light. To be specific, examples of the special light observation include a technique called narrow band imaging (NBI), a technique called infra-red imaging (IRI), a technique called auto fluorescence imaging (AFI), and a technique called photodynamic diagnosis (PDD).
In the NBI, states of blood vessels in a mucous membrane surface layer and a deeper layer are observed using difference in absorption by hemoglobin between narrow band illumination light having a center wavelength of 415 nm and narrow band illumination light having a center wavelength of 540 nm that are emitted thereto. The hemoglobin in the mucous membrane surface layer absorbs the light of 415 nm and the hemoglobin in the deeper layer absorbs the light of 540 nm.
In the IRI, a drug called indocyanine green (ICG) having an absorption peak at near infrared light of a wavelength of around 805 nm in blood is injected intravenously as a contrast agent and near infrared light having a center wavelength of 805 nm and near infrared light having a center wavelength of 940 nm are emitted to observe shadow of blood vessel portions in a mucous membrane lower layer by absorption of the light by the ICG and diagnose running states of blood vessels and lymphatic vessels. In the IRI, the intensity of the light having the center wavelength of 805 nm varies depending on presence and absence of a tumor.
In the AFI, a fluorescent image emitted from a subject is observed by previously administering a fluorescent agent into the subject and irradiating the subject with exciting light. Furthermore, a tumor portion is diagnosed by observing presence and absence of the fluorescent image and a shape thereof. Fluorescence from the fluorescent agent is emitted in the mucous membrane surface layer in a normal tissue whereas fluorescence from the fluorescent agent is significantly lowered when an accumulation of blood vessels or mucous membrane thickening due to lesions occurs in the mucous membrane surface layer.
In the PDD, an image on which cancer cells and normal cells are easy to be distinguished from each other is provided using the following characteristics. That is, when a solution of aminolevulinic acid (5-ALA) is dosed to a patient, it is metabolized by a blood material (heme) in a normal tissue in the body but it is not metabolized and is accumulated as a material called PpIX as an intermediate product thereof in the cancer cells. When the PpIX is irradiated with blue light (center wavelength of 410 nm), the PpIX emits fluorescence of red (peak wavelength of 630 nm). It should be noted that the normal cells emit blue light on reception of the irradiated blue light, for example, light of 460 nm on the bottom of the irradiated blue light.
As endoscope apparatuses capable of performing the special light observation, a dedicated endoscope apparatus and an endoscope apparatus using another imaging element for special light have been known. The dedicated endoscope apparatus, however, has a problem in that endoscopes for the normal observation and the special light observation need to be switched during surgery. On the other hand, the endoscope using another imaging element for the special light does not use pixel information of the imaging element for the special light in the normal observation and does not use pixel information of an imaging element for normal light in the special light observation. That is to say, the endoscope apparatus uses only one of the two imaging elements and the configuration thereof is not effective.
In the special light observation, in the NBI, imaging is performed using pixels receiving a light component of a wavelength band of blue (hereinafter, also referred to as B pixels) and pixels receiving a light component of a wavelength band of green (hereinafter, also referred to as G pixels). When a usual single-plate-type imaging element of the Bayer array is used, imaging is performed while the number of G pixels is half of the total number of pixels and the number of B pixels is quarter thereof, resulting in generation of an image deteriorated in resolution relative to the normal light.
In the IRI, a usual single-plate-type imaging element of the Bayer array performs imaging using infrared-sensitive regions of pixels receiving a light component of a wavelength band of red (hereinafter, also referred to as R pixels), the G pixels, and the B pixels. In this case, the B pixels have regions in which light receiving sensitivity to the wavelength band of infrared rays is low and the quarter of an acquired image is generated based on information provided by the low-sensitivity imaging, resulting in lowering of sensitivity.
In the AFI, a barrier filter for cutting light of a wavelength of equal to or lower than 500 nm needs to be provided on a light path of an imaging optical system and needs to be inserted or removed for switching between the AFI and the normal observation. When the insertion and removal of the barrier filter is difficult in terms of a space, a dedicated optical system and a dedicated imaging system need to be separately provided, resulting in size increase of the apparatus configuration. This causes a problem in that there is no choice but to employ a small-sized imaging element having the small number of pixels for the space.
In the PDD, imaging is performed using the R pixels and the B pixels. When the usual single-plate-type imaging element of the Bayer array is used, imaging is performed with the quarter of the total number of pixels for each of the R pixels and the B pixels, resulting in generation of an image deteriorated in resolution for the normal light.
For example, Japanese Patent Application Laid-open No. 2007-135951 discloses, as a single-plate-type imaging element, an imaging element in which the B pixels and pixels receiving a light component of a wavelength band of white (hereinafter, also referred to as W pixels), pixels receiving a light component of a wavelength band of cyan (hereinafter, also referred to as Cy pixels), or pixels receiving a light component of a wavelength band of magenta (hereinafter, also referred to as Mg pixels) are arranged, and the number of pixels receiving the light component of the wavelength band of green is equal to or more than the half of the total number of pixels and the number of pixels receiving the light component of the wavelength band of blue is equal to or more than the half of the number of pixels receiving the light component of the wavelength band of green.
In order to provide a finer observation image, imaging devices receiving observation light using a plurality of imaging elements have been known (for example, see Japanese Patent Application Laid-open No. 2015-116328). The imaging device as disclosed in Japanese Patent Application Laid-open No. 2015-116328 has the configuration in which a dichroic mirror reflecting a light component of the wavelength band of green and transmitting light components of the wavelength bands of red and blue, an imaging element receiving the light component reflected by the dichroic mirror, a filter transmitting the light component of the wavelength band of red, and a filter transmitting the light component of the wavelength band of blue are aligned, and imaging elements receiving the light components that have passed through the filters among the light components that have passed through the dichroic mirror are used to generate an image based on electric signals generated by the respective imaging elements.